In recent years, OpenFlow is known as a technology that can perform flexible packet transfer control that is not bounded by existing packet transfer or routing processing in which a known L2 switch, router or the like is used. OpenFlow is a technology that includes an OpenFlow controller (OFC) and an OpenFlow switch (OFS) and in which the OFC collectively manages route control and transfer control of a plurality of OFSs. The OFC sets, to each OFS, a flow table including match conditions for identifying a flow of a control target and information that defines a process to be execute such as, for example, transfer, disposal or field rewriting in the header for packets that satisfy the match conditions. It is to be noted that the flow table is set freely by an operation administrator of a network or a user and is set dynamically and programmably to each OFS using the OpenFlow protocol. Each OFS refers to the flow table to execute processing corresponding to a received packet.
In OpenFlow, in order to avoid a network disorder arising from a disorder of the OFC, the OFC is made redundant using a primary OFC and a secondary OFC. For example, the primary OFC monitors and controls a plurality of OFSs, and the secondary OFC monitors and controls the plurality of OFSs when the primary OFC suffers from a disorder. Meanwhile, each OFS periodically executes keepalive with the OFC that controls the own apparatus to detect a disorder of the OFC.
If each OFS detects a disorder of the primary OFC on the basis of a result of the monitoring of keepalive, then it switches the primary OFC to the secondary OFC. As a result, each OFS can recover the primary OFC from the disorder.
As examples of a prior art, Japanese Laid-open Patent Publication No. 2014-135614, Japanese Laid-open Patent Publication No. 2011-160363, Japanese Laid-open Patent Publication No. 2011-244095 and “OpenFlow Switch Specification Version 1.4.0,” Oct. 14, 2013, OPEN NETWORKING FOUNDATION are known.